1. Field of the Invention
The present invention is directed to satellite navigational systems such as the Global Positioning Satellite (GPS) System. More specifically, but without limitation thereto, the present invention is directed to a method of transmitting satellite positioning data to a remote GPS receiver from a base station.
2. Description of the Prior Art
A Global Positioning System (GPS) receiver typically stores satellite almanac data for each satellite of the GPS constellation in non-volatile memory. The satellite almanac data includes low precision orbital parameters for each of the GPS satellites in the constellation for determining which satellites are in view of a GPS receiver and to calculate approximate Doppler data for the satellites in view when attempting either autonomous fixes, that is, unassisted position calculations, or assisted fixes, before ephemeris information is available. The ephemeris data includes high precision orbital parameters, typically only for the GPS satellites in the constellation that are in view. The ephemeris data ages quickly. Slowly over time, the satellite almanac data becomes stale, requiring updated information. Also, the GPS constellation may change as new satellites are brought on line and old satellites are taken out of service.
Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of the following description of the illustrated embodiments.